Can someone explain to me (small words please, I'm feeling dumb today) why a small dome would not work on a rectilinear WA lens?

I'm considering trying a Sigma 8-16mm lens in a housing, and starting to research ports, and remember how much of a PITA the 8" Ike port was to pack.... Over/under shots are not enough motivator to stay big.

Can someone explain to me (small words please, I'm feeling dumb today) why a small dome would not work on a rectilinear WA lens?

I'm considering trying a Sigma 8-16mm lens in a housing, and starting to research ports, and remember how much of a PITA the 8" Ike port was to pack.... Over/under shots are not enough motivator to stay big.

A small dome will work on a rectilinear WA lens!

I cannot speak to other domes, but my domes work great with rectilinear lenses.

I cannot speak to other domes, but my domes work great with rectilinear lenses.

Barrywww.bareports.comwww.keywordworkflow.com

Barry:

Thanks for the answer. I saw the comment further up in this thread by someone else, maybe on the first page. I think (having now read Alex's article on the subject) that the poster might have simply meant that rectilinear WA lenses don't give you the same forced perspective in the middle of the frame as a fisheye, hence they're not as "useful" for CFWA type shots. But the wording I read seemed more like it was saying they didn't really work behind the small domes, which didn't make sense to me. Regardless of FE vs. Rect, if the lens 'focuses' well across the field of view (not always true, wide open) I'd think a dome in the right nodal location would work regardless of diameter. Glad you can confirm.

Unfortunately I'm probably looking at an Ikelite housing, so I won't be able to buy one of yours... I did see your link to Bob's site though so I'll likely ping him as I get my kit together. Thanks for helping me educate myself. I've been out of the water too long and am rarin' to get back in.

(EDIT): I just noticed another issue that might be a factor. The Tokina 10-17 supposedly focuses in to about 5.5 inches. The Sigma 8-16mm rectilinear (the lens I'm thinking of) only focuses in to a bit over 9 inches away. Would that be problematic as the dome got smaller, especially as a bulbous front element means no diopters are possible? Given the usual 1.5x diameter rule...I think the 6" dome might be the smallest I should consider after all...?

Thanks for the answer. I saw the comment further up in this thread by someone else, maybe on the first page. I think (having now read Alex's article on the subject) that the poster might have simply meant that rectilinear WA lenses don't give you the same forced perspective in the middle of the frame as a fisheye, hence they're not as "useful" for CFWA type shots.

I do not think you will have any problem with the forced perspective look with any extreme w/a lens that is focused to minimum distance. The image may not look as bulged in the center, but that can be a good thing.

Unfortunately I'm probably looking at an Ikelite housing, so I won't be able to buy one of yours... I did see your link to Bob's site though so I'll likely ping him as I get my kit together. Thanks for helping me educate myself. I've been out of the water too long and am rarin' to get back in.

I think you mean Bill's ports from uwcamera stuff.com? If so, he uses acrylic that I use and also duplicates my port shades for his deluxe shade so, his ports will work as good as mine, but for Ikelite.

(EDIT): I just noticed another issue that might be a factor. The Tokina 10-17 supposedly focuses in to about 5.5 inches. The Sigma 8-16mm rectilinear (the lens I'm thinking of) only focuses in to a bit over 9 inches away. Would that be problematic as the dome got smaller, especially as a bulbous front element means no diopters are possible? Given the usual 1.5x diameter rule...I think the 6" dome might be the smallest I should consider after all...?[/b]

I do not think you will have a problem with the close focus distance of your lens. What you are speaking of is your lens' ability to focus to infinity behind a dome port underwater. I read where someone wrote the virtual image is at 1.5X the radius at infinity, but I am not sure that is a 100% accepted distance by everyone. Through the years, I have always been told 2X the diameter of the port. Also remember that the focus distance is not from the end of the lens, but from the film or sensor plane which also adds distance.

I hope this information helps and does not confuse.Barrywww.bareports.comwww.keywordworkflow.com

Here, Wetpixel member Lill Haugen used a Bare dome port to win 1st place in the Norwegian Underwater Photo Championships 2011. Congratulations Lill!!

This shot shows how well a small dome handles CFWA images.

The small dome, like the Bare dome port will also work well with wide angle that is not Close Focus Wide Angle as can be seen by my image below.

Seems there are lots of misconceptions about the value of a smaller dome. As can be seen above, the smaller dome works well for large scenics as well as CFWA. The only downside I have found to a smaller dome is using them for over and under shots.

Your photo links aren't working for me right this second, but that may be work-computer (firewall) related.

I did get a dome from Bill @ UWcamerastuff. Have just tested it quickly in a pool so far, but was able to focus as close as I felt I could safely move a dome to a subject, and corner clarity looks fairly good so far (using a Sigma 8-16mm). Will post some test shots in a couple of weeks on my flickr page if I can.

First test shots were fixed 8mm only before I figured out how to rig a zoom sleeve (turns out the Ike 'standard' sleeve with NO clamp can 'grab' the Sigma 8-16mm zoom rubber grip toothing, if you notch it back a tad so it doesn't also impinge where there are similar rubber teethy glued to the 'fixed' collar of the lens). Haven't been back in the water to test it sleeved as well so I can see how the port works with different zoom distances.

Your photo links aren't working for me right this second, but that may be work-computer (firewall) related.

Have just tested it quickly in a pool so far, but was able to focus as close as I felt I could safely move a dome to a subject, and corner clarity looks fairly good so far (using a Sigma 8-16mm). Will post some test shots in a couple of weeks on my flickr page if I can.

Hi Rtrski,

Did you ever post your shots on Flicker? If so how do I find them and how did the port work for you?

Sorry for the slow response, just got back from Dominica late last week and getting back into the work grind.

Photographically results of the trip were mixed - my skill, not either the DM guidance, equipment, or subject matter! I failed to think thru just how hard even a little 'snow' in the water makes truly wide angle shots, and as this was my first trip with strobes larger than Ike DS50's I've got a lot yet to learn about strobe aiming.

I've still got a huge number to process but the first few are up. My main Flickr page is www.flickr.com/photos/rtrski, there's a separate set for Dominica 2012 you can probably find by clicking thru various options (I hate flickr defaulting to a 'photostream' view, but what can you do).

Here's a couple examples at 8-9mm behind the dome. I know I disabled the 'full size' download so this is downsized significantly, but despite the obvious rectilinear 'distortion' in the corners the corner sharpness looks pretty good to my eye. Shot at f11...first image isn't cropped, second is but bottom right corner of the frame I think was the original outer corner.

Overall shots were from either the 8-16mm behind Blibecap's minidome or a 17-70mm with +2 diopter behind the typical Ike 6" dome, so I shouldn't have wasted time playing 'macro' but couldn't resist on occasion.

I did some diving in Cozumel and used the dome port made by Barry Guimbellot. I used it on my Nexus housing with the Tokina 10-17 lens on a Nikon D2x camera. It is so much easier to pack and use the small dome rather than the large dome I originally purchased from Nexus. It also doesn't make the housing so buoyant in the front like the big dome does which makes it much more comfortable to use underwater. I'm usually having to twist downward with my wrists to keep the housing level with the big dome port on so for someone with carpal tunnel tendencies it keeps the stress on the wrists much lower. It makes for really sharp pictures edge to edge and is a lot easier to use besides being a lot less expensive. I've attached some pics I took with it. Pics are not cropped

Is it possible to make the dome and use it as a wet lens for my s95 with canon housing... i got a 67mm filter thread adapter already

But i will like to do a wide angle shot as the 28mm on the s95 is abit not so wide angle underwater...

I do not think my dome can be used on your s95 Canon housing, even though you do not mention what housing you have. There is an extension built into my ports that will most likely cause your lens to vignette. The hole diameter in the back of the smallest, M5 size port, is 100 mm, which is much larger than your adapter.